Electric contact



Patented Apr. 16,1940

PATENT OFFICE EIEUIRIC CONTACT UNITED STATES poration of Delaware NoDrawing. Application June 5, 1939, Serial No. 277,494

6 Claims.

This invention relates to a new silver electric contact and is concernedmore particularly with an electric contact which has improved physicaland electrical characteristics.

It is one of the objects of the invention to provide a silver basecontact material which can be used for an electrical make and breakcontact; retaining low contact resistance, having low material transferand having increased resistance 10 to welding and sticking underelectrical loads.

. Another object of the invention is to provide a new silver basecontact alloy which has improved physical properties, such as hardnessand tensile strength, and retains a high ductility.

It is a further object to provide a material which shows considerableimprovements as far as corrosion resistance is concerned.

Other objects of the invention will be apparent from the followingdescription taken in connec- 0 tion with the appended claims. Thepresent invention comprises a combination of elements, methods ofmanufacture and the product thereof, brought out and exemplified in thedisclosure hereinafter set forth, the scope of the inventio beingindicated in the appended claims.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the method ofprocedure and the combination of elements, without departing from thespirit of the invention.

The present invention comprises an electric contact of silver withberyllium, and a third element, taken from the same group, to which 35beryllium belongs, namely, magnesium, zinc and cadmium.

In the formation of the new contact alloy, it is preferable to provide acomposition of the mate- 0 rials specified in the following proportions:

} Per cent Beryllium; .05- 4 Metal taken from the second group of theperiodic system, comprising magnesium,

45 zinc and cadmium Silver Substantially the balance titanium,zirconium,

located at approximately .97% of beryllium, an alloy of this compositionhaving a melting point of 881 degrees C. The alpha solid solubility ofberyllium in silver is quite small and at the eutectic temperature, doesnot exceed .35% ii beryllium. This solid solubility furthermoredecreases with temperature which indicates that the alloys of this typecan be improved by heat treating as far as electrical conductivity isconcerned, and also as far-as hardness and tensile properties areconcerned. The increase in properties, however, with such smallpercentages of beryllium present, is comparatively small. The fact thatthe system is of an eutectic nature, however, results in a materialwhich retains a rather high electrical conductivity, because theelectrical conductivity is lowered primarily if a solid solution isformed; therefore, in our tests, we have found that a material of almostthe eutectic composition and which contained .94% b beryllium, balancesilver, showed in the as cast condition, an electrical conductivity of67.2% I. A. C. S. With an increase of the beryllium content, the soliduscurve is raised very steeply and an alloy containing about 4% berylliumhas 25 a solidus which is located above 1000 degrees C. The elementswhich are contemplated as additions in the present disclosure,arecadmiurn, magnesium and zinc. There is considerable similarity in thediagrams of silver-cadmium, silver-magnesium and silver-zinc. All threeof these metals, namely, magnesium, zinc and cadmium, form an alphasolution with silver, the alpha range being the smallest in thesilvermagnesium system, and the highest in the silvercadmium system. Inaddition to the alpha range, a number of other phases are'formed thatare usually identified by such letters as beta, gamma, delta, and in thecase of silver-cadmium and silver-zinc, epsilon, and eta. The presentinven- 40 tion, however, considers the addition of the elements ofmagnesium, .cadmium and zinc,

primarily in their alpha range or possibly in the beta range. a

In preparing the alloys, it is desirable to add beryllium in the. formof a silver-beryllium master alloy containing approximately 4-6% ofberyllium. The master alloys which were used in the present experimentscontained, in one case, 4% of beryllium, and had a Rockwell F hardnessof -81, and in the other case, 5% of beryllium, which alloy had aRockwell F hardness of 86. The materials of the second group of theperiodic system, namely, magnesium, zinc and The master alloys wereprepared either by melting or by pressed powder methods.

We have investigated a. series of compositions and have found that thefollowing alloys, which are given by way of example only, have showngood physical properties and also good electrical properties:

Per cent (1) Beryllium .05- 4 Metal taken from the second group of theperiodic system, comprising magnesium, zinc and cadmium .1 5 SilverBalance (2) Beryllium .05- 4 Metal taken from the second group of theperiodic system, comprising magnesium, zinc and cadmium 1- 8 SilverBalance (3) Beryllium .05- 4 Metal taken from the second group of theperiodic system, comprising magnesium, zinc and cadmiumc 1-25 SilverBalance (4) Beryllium .05- 4 Metal taken from the second group of theperiodic system, comprising magnesium, zinc and cadmium 5-25 SilverBalance (5) Beryllium .75- 2 Metal of the second group of the periodicsystem, comprising magnesium, zinc and cadmium 1- 10 Silver Balance Analloy containing about .91% beryllium and 6-7% cadmium, showed in thecast condition 40% electrical conductivity and a cast hardness of 17Rockwell F. After swaging, 25%, this hardness was increased to 89Rockwell F. This material showed a very high density in the as castcondition.

An alloy containing approximately .9-1% and 3 4% zinc, showed anelectrical conductivity in the cast condition of 26.1%, a cast hardnessof 37 Rockwell F, which was raised to 92- Rockwell F by 25% coldswaging.

An alloy approximately beryllium and /z%-3% of magnesium, showed anelectrical conductivity in the as cast condition of 22.7%, a casthardness of 43 Rockwell F, which was increased to Rockwell F, by 25%cold swaging. This latter alloy had a specific gravity of approximately9 grams peT cc., which is considerably below that of fine silver, thespecific gravity of which is 10.5. This is due to the lower specificgravity, both of magnesium and beryllium.

In adding cadmium, zinc and magnesium to the alloys of the presentinvention, more consistent results are obtained if the substitution ofelements is carried out by volume percentage, rather than weightpercentage. This automati= cally indicates that a smaller percentage ofmagnesium added, corresponds to a higher percentage of, for instance,cadmium, because the speciilc gravities of the two materials are quitedifferent. The specific gravity of magnesium, for instance, is 1.74,while the specific gravity of cadmium is 8.648. This is a ratio of about1:5. In other words, in order to have the same volume percentage ofmagnesium and cadmium present, in the alloys of the present invention,it would be necessary, in one case, to add about 3 weight per cent ofmagnesium and in the other case, 15 weight per cent, of cadmium. Thespecific gravity of zinc is 7.14 and the ratio of speciflc gravities ofmagnesium to zinc, corresponds to approximately 1:4. The constitutionaldiagrams are usually plotted in weight per cent. By changing the weightpercent to volume percent, it can be found that the alpha solidsolutions of magnesium in silver, or zinc in silver, or cadmium insilver are very nearly-the same if they are plotted in volume percentrather than in weight percent.

The corrosion resistance of silver alloys is highest in the alpha solidsolution range, and therefore it is desirable to add beryllium to thealpha solid solutions of magnesium in silver, zinc in silver and cadmiumin silver.

A comparison test was conducted, wherein contacts of similar physicaldimensions were tested on a resistive inductive circuit at 470 cyclesper minute and wherein current flowing in the circuit was increasedperiodically to obtain definite current values in the nature describedabove in comparison with contact materials produced in the prior art.The amount of material transfer of one contact to another was found tobe considerably less' than materials of the prior art, not containing acombination of beryllium and a metal taken from the group of magnesium,zinc and cadmium.

At the same time, it was found that after completion of the tests, thecontact resistance of the material was quite low. The actual testsshowed a contact resistance after completion of the tests, of .40milliohm, in the case of the beryllium-cadmium alloy. In the case of theberyllium-zinc alloy the contact resistance was .70 milliohm aftercompletion of the tests, and in the case of the beryllium-magnesiumalloy the contact resistance was .80 after completion of the test. Theberyllium-cadmium alloy showed the highest critical current values atwhich the material would not stick.

The alloys of the present invention have been found to have excellentfree machining properties for the production of commercial parts wherehigh speed production and corrosion resistance are required. r While thepresent invention as to its objects and advantages has been describedherein as carriedout in specific embodiments thereof, it is not desiredto be limited thereby, but it is intended to cover. the inventionbroadly, within the spirit and scope of the appended claims.

What is claimed is:

1. An electric contact consisting of beryllium, .05-4%, 3. metal takenfrom the second group of the periodic system, comprising magnesium, zincand cadmium, .1-25%, silver, substantially the balance.

2. An electric contact consisting of beryllium, 05-4%, and a metal takenfrom the second group of the periodic system, comprising magnesium, zincand cadmium, .1-5%, silver substantially the balance.

3. An electric contact consisting of beryllium, 05-4%, and a metal takenfrom the second group of the periodic system, comprising magnesium, zincand cadmium, 1'-8%, and silver, substantially the balance.

4. An electric contact consisting of beryllium,

.054%, and a metal taken from the second group of the periodic system,comprising magnesium, zinc and cadmium, 1-25%, silver substantially thebalance,

5. An electric contact consisting of beryllium,

.054%, and a metal taken from the second group group of the periodicsystem, comprising magof the periodic system, comprising magnesium,nesium, zinc and cadmium, 140%, silver subzinc and cadmium, 5-25%,silver substantially stantially the balance. the balance. FRANZ R.HENSEL.

5 6. An electric contact consisting of beryllium, KENNETH L. EMMERT. 5

.75-2%%, and a metal taken from the second JAMES W. WIGGS.

